D is the diameter of internal sheath and d is diameter of core, the most economical conductor  diameter d is

Q. D is the diameter of internal sheath and d is diameter of core, the most economical conductor  diameter d is

A.            d = D

B.            d = 1/D

C.            d = D/ 2.718

D.            d = D x 2.718

Answer: d = D/ 2.718